The present invention relates to a control system for use in multi-cylinder internal combustion engines, and more particularly to a misfire detection apparatus for detecting the occurrence of misfire in the internal combustion engine.
A known system for detecting misfire in an internal combustion engine is known an apparatus arranged to detect the rotational speeds of a crankshaft before and after the expansion stroke of a reciprocating internal combustion engine and to determine a misfire when the difference between the detected rotational speeds is below a predetermined value, as disclosed in the Japanese Patent Provisional Publication No. 58-19532. More specifically, on the basis of the fact that the crankshaft speed in the expansion stroke is higher than the crankshaft speed in the compression stroke when the engine is in the normal ignition state and the difference therebetween substantially becomes zero in response to occurrence of the misfire, the misfire is determined when the rotational speed difference is below a predetermined value, i.e., when the crankshaft is not accelerated in the expansion stroke. Further, as disclosed in the Japanese Patent provisional Publication No. 58-51243, another known technique involves detecting the fluctuation of the engine speed so as to calculate the standard deviation to determine the misfire of the engine when the standard deviation is great.
There is a problem which arises with such apparatus, however, in that the crankshaft rotational speed becomes unstable when a motor vehicle runs on a irregular road surface whereby there is the possibility that the misfire is determined in error irrespective of the normal ignition. That is, the contact state between the wheel and the road surface becomes unstable due to the irregularity of the road and causes the load on the internal combustion engine to vary, impeding the normal rotation of the crankshaft. In addition, the impediment of the normal crankshaft rotation causes rotation fluctuation, making it difficult to accurately detect the misfire of the internal combustion engine.